Sub-surface Drainage

Water normally reaches the sub-surface due to capillary action, seepage from adjacent areas, or percolation of rainwater. When water reaches the sub-surface, it immediately affects the stability of the formation. The situation becomes worse particularly if the soil is bad. A variety of problems arise due to the proximity of the water to the subgrade. The nature of the problems faced and the remedial measures for the same have been discussed in detail in Chapter 9.

The various sub-drainage systems used under different conditions are briefly summarized here.

Provision of inverted filter Some sub-drainage systems consist of a blanket of a non-cohesive graded material, which acts as a capillary break (Fig. 9.3 of Chapter 9).

Paving of catch water drains The entrance of water into the subgrade can be checked by constructing effective catch water drains that are duly paved.

Provision of sand piling Some drainage systems are provided with an adequate number of sand piles of a diameter of about 20 cm. This improves sub-surface drainage (Fig. 9.4 of Chapter 9).

Drainage of water pockets by perforated pipe Perforated pipes with a diameter of about 30 cm are provided at appropriate places to drain off the water pockets (Fig. 9.5 of Chapter 9).

Cement grouting Cement can be used to grout the water pockets so as to ease the situation.

Drainage of water pockets by puncturing holes In special situations where water is trapped in ballast pockets because of an impervious layer that lies over a good pervious layer, puncturing holes into the impervious layer can help drain away the water (Fig. 9.6 of Chapter 9).

Summary

The presence of water can reduce the stability and strength of the track or erode the banks of an embankment. The lifespan of a track can be considerably increased by providing a proper drainage system. Whatever be the source of water entering the track, its removal from the track should be quick and effective. In the case of soft soils, sub-surface drainage may be necessary to keep the track safe.

Review Questions

1. Why is it necessary to provide adequate drainage facility for a railway track? Suggest remedial measures to solve the following problems that occur due to poor drainage.

(a) Clogging of the ballast because of wet earth

(b) Sinking of ballast into the wet earth

2. What are the requirements of a good track drainage system? How can a good drainage systems be provided on railway tracks?

3. Describe the drainage systems required for the following areas in detail.